This invention relates to polymers comprising photo-addressable side groups, in which a high level of birefringence can be induced by irradiation, so that they are suitable for the storage of information which is provided optically or are suitable as passive or optically switchable components.
Various polymers comprising photochromic groups are known from the literature: the special peculiarity thereof is that their optical properties, such as absorption, emission, reflection, birefringence and scattering, can be induced by light and can be varied reversibly. Polymers of this type have a special branched structure: side groups which are capable of absorbing electromagnetic radiation are seatedxe2x80x94via parts of molecules which act as spacersxe2x80x94on a linear backbone. The interest of experts in this field has recently been directed towards side group polymers such as these which comprise side groups of different types, one type of which is capable of absorbing electromagnetic radiation whilst the other type is a mesogenic group, the shape of which is anisotropic. Liquid crystalline side group polymers of this type are described in U.S. Pat. Nos. 4,631,328 and 4,943,617, for example. In their unoriented state, films of these polymers are turbid and scatter light; these films do not become clear and transparent until they are aligned.
Amorphous polymers which are suitable for storing optical information are known from DE-OS 38 10 722 and U.S. Pat. No. 5,173,381. These have the technical advantage that films made of these polymers exhibit usable optical properties immediately after they are produced.
Homopolymers are seldom mentioned in this connection. EP-A 617 110 describes azo-containing carbaminates which are rendered polymerisable by N-acylation with (meth)acrylic acid. In actuality, homopolymers are generally inferior to copolymers.
The only processes which have been described hitherto for the reversible storage of information are those where deletion of the information is effected by raising the temperature, and can be effected both by heat and by light. Moreover, deletion by light can exhibit the advantage that the process is limited to a defined location, which is why this variant is preferred. In general, it can be stated that on raising the temperature the property of retaining stored information is lost. The known compounds therefore have the disadvantage that the birefringence effects which are written in are not thermally stable. At elevated temperatures. particularly at temperatures approaching the glass transition temperature, birefringence becomes less pronounced and finally disappears completely. There is therefore a need for information storage media for which the stability of written information is as insensitive to temperature as possible.
Surprisingly, it has now been found that superior side chain polymers which are suitable for the production of photo-addressable information storage media can be produced if monomers are homopolymerised, which
contain groupings which are at least trinuclear, which are capable of absorbing the electromagnetic radiation of visible light, and which are structured so that in their thermodynamically stable state they are distended and strongly anisometric.
wherein the at least trinuclear groupings comprise at least one, preferably at least two, electron-attracting substituent(s) which give(s) rise to a dipole moment which forms an angle of at least 20xc2x0, preferably at least 30xc2x0, with the longitudinal axis of the at least trinuclear groupings.
Thermally stable grey scales can be written into these new polymers under the effect of light.
In principle, at least two methods of influencing the dipole moment are possible, namely
substitution with lateral, electron-attracting substituents which are disposed unsymmetrically with respect to the longitudinal axis of the grouping, and
the use of nucleus-linking polar groups, the dipole moments of which do not point in the direction of their longitudinal axis.
Groups which are capable of forming hydrogen bonds with each other, such as xe2x80x94NHxe2x80x94COxe2x80x94 and xe2x80x94OCxe2x80x94NHxe2x80x94 for example, are particularly preferred in this respect.
The expression xe2x80x9celectromagnetic radiation of visible lightxe2x80x9d should be understood to mean light with a wavelength range from 350 to 750 nm.
The expression xe2x80x9cthermodynamically stable statexe2x80x9d should be understood in the sense of the present invention to mean the lowest energy configuration, such as that which occurs in the dark in a dissolved state in an organic solvent, for example. When cis/trans isomerism exists, such as that which occurs with stilbenes and azo compounds for example, the trans isomer is the isomer of lower energy in each case. The configuration which is present can be determined spectroscopically from the absorption bands.
xe2x80x9cDistendedxe2x80x9d in the sense of the present invention is to be understood to mean a state in which the at least trinuclear groupings are situated within a cylinder with a length/diameter ratio of 2.5, preferably 3, wherein the length of the cylinder is identical to the length of the at least trinuclear grouping.
xe2x80x9cStrictly anisometricxe2x80x9d in the sense of the present invention means a structure in which none of the nuclei is directly or indirectly bonded (i.e. via a bonding group without a nucleus) to the next nucleus, i.e. it preferably (for trinuclear groupings) means a structure where the middle nucleus is a 6-membered ring which is directly or indirectly bonded via its 1- and 4-positions to the adjacent nuclei.
xe2x80x9cElectron-attracting substituentxe2x80x9d in the sense of the present invention is to be understood to mean substituents which reduce the basicity, i.e. the electron density, of the nucleus on which they are situated, due to induction and/or mesomeric effects. These substituents preferably comprise alkylcarbonyl, carboxyl, alkoxycarbonyl, carbamido, carboxylamino, cyano, nitro and ammonium, andxe2x80x94less preferablyxe2x80x94comprise the halogens.
xe2x80x9cLateralxe2x80x9d in the sense of the present invention can be explained by citing the example of an azobenzene group, and denotes that the substituent forms an angle with the longitudinal axis of the azobenzene and is therefore situated in the o- and/or m-position, whilst a substituent in the p-position is not considered as being xe2x80x9clateralxe2x80x9d in the sense of the invention. If a phenyl radical of the azobenzene is replaced by a five-membered ring, for example, the substituents are xe2x80x9clateralxe2x80x9d in all conceivable positions, because on a five-membered ring there is no position corresponding to the p-position on a 6-membered ring.
In principle, all groups which contain carboxyl groups are suitable as nucleus-linking polar groups, the dipole moment of which is at least 200. This can be well illustrated by using the amide group as an example: 
The orientation of the dipole moment of the carboxyl group forms an angle xcex1 with the longitudinal axis which is at least 20xc2x0.
The present invention also relates to homopolymers, formed from monomers which
contain groupings which are at least trinuclear, which are capable of absorbing the electromagnetic radiation of visible light, and which are structured so that in their thermodynamically stable state they are distended and strongly anisometric,
wherein the at least trinuclear groupings comprise at least one electron-attracting substituent which gives rise to a dipole moment which forms an angle of at least 20xc2x0 with the longitudinal axis of the at least trinuclear groupings.
The preferred groupings which are at least trinuclear are those which contain at least two aromatic nuclei.
The preferred polymers according to the invention contain, on a main chain which acts as a backbone, covalently bonded side groups which branch therefrom, of formula
xe2x80x94Sxe2x80x94Txe2x80x94Qxe2x80x94Exe2x80x83xe2x80x83(1),
wherein
S denotes oxygen, sulphur or NR1.
R1 denotes hydrogen or C1-C4 alkyl.
T denotes a (CH2)n radical, which can optionally be interrupted by xe2x80x94Oxe2x80x94, xe2x80x94NR1xe2x80x94 or xe2x80x94OSiR12Oxe2x80x94 and/or which can optionally be substituted by methyl or ethyl,
n denotes the numbers 2, 3 or 4,
Q denotes a radical comprising two bonds, and
E denotes an at least trinuclear grouping which comprises the features according to the claims.
The function of the radical T is to ensure a certain spacing of the side group from the chain which acts as the backbone. It is therefore also termed a xe2x80x9cspacerxe2x80x9d.
The radical Q links the terminal group E to the spacer T, which itself forms the bond to the main chain via bonding element S. The special feature of group Q is its influence firstly on E and secondly on the adjacent groups.
The preferred radicals Q comprise the groups xe2x80x94Sxe2x80x94, SO2xe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CONR1xe2x80x94, xe2x80x94NR1xe2x80x94COxe2x80x94, xe2x80x94NR1xe2x80x94 and (CH2)m, where m=1 or 2.
The at least trinuclear groupings E contain at least one nucleus-linking group which is suitable for a photo-induced change in configuration, such as 
In addition to at least one group of variable configuration, the groupings E also contain other nucleus-linking groups, such as xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CONR1xe2x80x94, xe2x80x94NR1COxe2x80x94 or a direct bond, wherein R1 is preferably H and direct bonds are less preferred.
The at least 3 nuclei of E can each represent a 5- or 6-membered cycloaliphatic ring or a naphthalene radical, with the proviso that at least two nuclei, and preferably at least three nuclei, are aromatic.
Nuclei of E which are particularly preferred include 2,6-naphthylene and 1,4-phenylene, as well as heterocyclic radicals of structures 
5-membered ring systems can be carbocyclic, but are preferably heteroaromatic and contain up to 3 hetero atoms, preferably from the series comprising S, N, O. Examples of suitable representatives include thiophene, thiazole, oxazole, triazole, oxadiazole and thiadiazole. Heterocycles comprising 2 hetero atoms are particular preferred.
The preferred groupings E contain cinnamic acid or stilbene radicals and azo dye radicals or analogues of a heterocyclic type, preferably mono- and diazo dye radicals.
The groupings E should be polarised. As described above, said polarisation can be effected by substitution with electron-attracting lateral substituents. The preferred substituents are those which have Hammett values of at least 0.5. The "sgr" values are known from the literature; see C. Hansch, A. Leo, R. W. Taft, Chem. Rev. 1991 91 (165-195). If the nuclei are multiply-substituted, the number of substituents in each case depends on the number of possible positions of substitution, on the options for incorporating the substituents and on the properties of the substituted systems. The 2,4- and 3,4-positions on 6-membered rings are preferred; the preferred substituents are cyano and nitro.
Aromatic nuclei which are suitable for B preferably contain 6 to 14 C atoms in their aromatic ring, which can be singly- or multiply-substituted by C1-C12 alkyl, C1-C12 alkoxy, hydroxy, halogen (particularly F, Cl or Br), amino, nitro, trifluoromethyl, cyano, carboxy, COOR (Rxe2x95x90C1-C6 alkyl, cyclohexyl, benzyl, phenyl), C5-C12 cycloalkyl, C1-C12 alkylthio, C1-C6 alkylsulphonyl, C6-C12 arylsulphonyl, aminosulphonyl, C1-C6 alkylaminosulphonyl, phenylaminosulphonyl, aminocarbonyl, C1-C6 alkylamino-carbonyl, phenylaminocarbonyl, C1-C4 alkylamino, di-C1-C4 alkylamino, phenylamino, C1-C5 acylamino, C1-C4 alkylsulphonylamino, mono- or di-C1-C4 alkylaminocarbonylamino, C1-C4 alkoxycarbonylamino or trifluoromethyl-sulphonyl.
Heterocyclic nuclei which are suitable for E preferably contain 5 to 14 ring atoms, 1 to 4 of which are hetero atoms from the series comprising nitrogen, oxygen and sulphur, wherein the heterocyclic ring system can be singly- or multiply-substituted by C1-C12 alkyl, C1-C12 alkoxy, hydroxy, halogen (particularly F, Cl or Br), amino, nitro, trifluoromethyl, cyano, carboxy, COOR (Rxe2x95x90C1-C6 alkyl, cyclohexyl, benzyl, phenyl), C5-C12 cycloalkyl, C1-C12 alkylthio, C1-C6 alkylsulphonyl, C6-C12 arylsulphonyl, aminosulphonyl, C1-C6 alkylaminosulphonyl, phenylaminosulphonyl, aminocarbonyl, C1-C6 alkylamino-carbonyl, phenylaminocarbonyl, C1-C4 alkylamino, di-C1-C4 alkylamino, phenylamino, C1-C5 acylamino, C1-C4 alkylsulphonylarnino, mono- or di-C1-C4 alkylaminocarbonylamino, C1-C4 alkoxycarbonylamino or trifluoromethyl-sulphonyl.
Particularly preferred groupings E contain the following binuclear partial radicals: either one aromatic nucleus and one heterocyclic nucleus or two aromatic nuclei.
The preferred binuclear partial radicals are azobenzene radicals of formula 
wherein
R represents a bond or nitro, or preferably represents a 4-substituted benzamido or cyano, and the rings A and B can be substituted in addition. If R represents cyano or nitro, ring A is preferably substituted in addition, wherein the substituent should have a "sgr" value of at least 0.5.
Azobenzene radicals which are particularly preferred correspond to the formula 
wherein
R2 to R6, independently of each other, represent hydrogen, chlorine, bromine, trifluoromethyl, methoxy, SO2CH3, SO2CF3, SO2NH2, preferably CN, 4-substituted benzamido or nitro, preferably with the proviso that at least two of these radicals are not hydrogen, wherein
R4 can additionally denote a single bond, and
R7 to R10, independently of each other, denote hydrogen, chlorine or methyl.
If there is multiple substitution of ring A, the 2,4- and 3,4-positions are preferred.
Therefore, the preferred groupings E correspond to the formula 
wherein
R2 to R6 and R7 to R10 have the meanings given above, and
R2xe2x80x2 to R6xe2x80x2 the have meanings of R2 to R6, but are independent thereof.
Other binuclear partial radicals correspond to the formula 
wherein
K, L and M, independently of each other, denote the atoms N, S or O, or optionally denote xe2x80x94CH2xe2x80x94 or xe2x80x94CHxe2x95x90, with the proviso that at least of one of the members K, L or M is a hetero atom and ring A is saturated or contains 1 or 2 double bonds, and
R2, and R7 to R10, independently of each other, have the meanings given above.
Ring A preferably represents a thiophene, thiazole, oxazole, triazole, oxadiazole or thiadiazole radical.
Other preferred groups E correspond to the formula 
wherein
R2 to R10 and R2xe2x80x2 to R6xe2x80x2 have the meanings given above.
A common feature of the above formulae is that substitution of ring A in the 4-, 2,4- and 3,4-positions is particularly preferred.
Groupings E which are particularly preferred correspond to the formulae: 
The polymers which are preferred according to the invention solely contain recurring units comprising side groups I, and preferably contain those of formula 
where Rxe2x95x90H, or preferably where Rxe2x95x90methyl.
The corresponding preferred monomers for the introduction of side groups I therefore correspond to the formula 
The main chain of the side group polymers is therefore formed solely from monomers which comprise side groups (I).
The polymers according to the invention preferably have glass transition temperatures Tg of at least 40xc2x0 C. The glass transition temperature can be determined as described by B. Vollmer, Grundrixcex2 der Makromolekularen Chemie, pages 406 to 410, Springer-Verlag, Heidelberg 1962, for example.
In general, the polymers according to the invention have a molecular weight, determined as the weight average molecular weight, from 3000 to 2,000,000, preferably 5000 to 1,500,000, as determined by gel permeation chromatography (calibrated with polystyrene).
Due to the structure of the polymers, the intermolecular interactions of structural elements (I) are such that the formation of liquid crystalline states of order is suppressed, and optically isotropic, transparent, non-scattering films can be produced. On the other hand, the intermolecular interactions are nevertheless sufficiently strong so that irradiation with polarised light results in a photochemically induced, cooperative, directional reorientation process of the side groups.
Extremely high levels of optical anisotropy can be induced in the optically isotropic, amorphous polymers according to the invention by irradiating them with polarised light. The measured values of the change in birefringence range between 0.05 and 0.08.
The light which is preferably used is linearly polarised light, the wavelength of which falls within the region of the absorption bands of the side groups.
The production of side group monomers and the polymerisation thereof can be effected by methods which are known from the literature; see, for example, Makromolekulare Chemie 185, 1327-1334 (1984), SU 887 574, Europ. Polym. J. 18, 651 (1982) and Liq. Cryst. 2, 195 (1987), DD 276 297, and DE-OS 28 31 909 and 38 08 430. The polymers according to the invention are generally produced by radical-initiated polymerisation in suitable solvents, e.g. in aromatic hydrocarbons such as toluene or xylene, in aromatic halogenated hydrocarbons such as chlorobenzene, in ethers such as tetrahydrofuran or dioxane, in ketones such as acetone or cycloohexanone, and/or in dimethylformamide. in the presence of radical-forming polymerisation initiators. e.g. azobis(isobutyronitrile) or benzoyl peroxide, at elevated temperatures, generally from 40 to 70xc2x0 C. if possible under water and with the exclusion of light. They can be isolated by precipitation in suitable media, e.g. methanol. The products can be purified by re-precipitation, e.g. with chloroform/methanol.
Isotropic films can be produced without costly orientation processes being necessary for which external fields and/or surface effects are required. They can be produced on substrates, by spin-coating, immersion, casting or by other coating methods which are easily controlled technologically, by pressing or flowing them between transparent plates, or can readily be produced as self-supporting films by casting or extrusion. Films such as these can be produced by sudden cooling, i.e. by employing a cooling rate  greater than 100 K/min, or can also be produced by rapidly stripping the solvent from liquid crystalline polymers which contain structural elements of the type described above.
The film thickness of films such as these preferably ranges between 0.1 xcexcm and 1 mm, particularly between 0.1 and 100 xcexcm.
When they are in their glassy state, the side group polymers according to the invention are optically isotropic, amorphous, transparent and do not scatter light, and are capable of forming self-supporting films.
However, they are preferably deposited on support materials, for example on glass or on plastics films. This can be effected by various known techniques, wherein the process is selected accordingly, depending on whether a thick or a thin film is required. Thin films can be produced, for example, by spin-coating or by doctor blade from solutions or from the melt, thicker layers can be produced by filling prefabricated cells, or by melt pressing or extrusion methods.
The polymers can be used for the storage of digital or analogue data in the widest sense, e.g. for optical signal processing, for Fourier transformation and convolution or for the coherent optical correlation technique. The lateral resolution is limited by the wavelength of the light used for writing. It enables a pixel size from 0.45 to 3000 xcexcm to be obtained. A pixel size from 0.5 to 30 xcexcm is preferred.
This property makes the polymers particularly suitable for the processing of images and for information processing by means of holograms, the reproduction of which can be effected by illumination with a reference beam. Similarly, the interference pattern of monochromatic light sources with a constant phase relationship can be stored. Three-dimensional holographic images can be stored correspondingly. Read-out is effected by illuminating the hologram with monochromatic coherent light. A storage density which is higher than that of a purely binary system can be achieved due to the relationship between the electric vector of the light and the preferred direction, which is associated therewith, in the storage medium. In analogue storage, values of the grey scale can be continuously adjusted, as can the local resolution thereof. Read-out of stored analogue information is effected in polarised light, wherein a negative or positive image can be retrieved depending on the position of the polarisers. The contrast between two polarisers which is produced by the phase shift between the ordinary and the extraordinary beam can firstly be used, wherein the planes of the polarisers advantageously form an angle of 45xc2x0 to the plane of polarisation of the inscribing light and the plane of polarisation of the analyser is either perpendicular or parallel to that of the polariser. Another possibility is the detection of the angle of deviation of the read-out light which is caused by the induced birefringence.
The polymers can be used as optical components which can be passive or which can be actively switchable, particularly for holographic optics. Thus the high extent of light-induced optical anisotropy can be used for the electrical modulation of the intensity and/or of the state of polarisation of light. Components which have imaging properties which are comparable with those of lenses or gratings can accordingly be produced from a polymer film by a holographic structuring process.
Therefore the present invention further relates to the use of the polymers described above for optical components.
Monomers IX are novel. Therefore, the present invention also relates to monomers IX.
Monomers IX can be produced by analogy with known reactions, e.g. by
A) the reaction of acid chlorides of formula 
xe2x80x83with 4-amino-binucleus compounds, e.g. 4-aminoazobenzenes, to form monomer IX, e.g. to form the compound of Example 2.1.1;
B)
1. By the condensation of
a) 1,4-diamino nuclei, e.g. 1,4-phenylenediamine, with
b) nucleus-acid chlorides, e.g. p-nitrobenzoyl chloride, to form
c) a p-(nucleus-carboxamino)-nucleus-amine, e.g. N-(p-nitrobenzoyl)-1,4-phenylenediamine
2. Diazotisation of 1 c) and
3. Coupling with a compound of formula 
xe2x80x83e.g. (meth)acrylic acid-1-(N-methylanilino)-ethyl ester, to form monomer IX, e.g. to form the compound of Example 2.4;
C)
1. diazotisation of a 4-amino binucleus, e.g. 4-aminoazobenzene,
2. Coupling with the (meth)acrylic acid ester 
xe2x80x83e.g. with (meth)acrylic acid-1-(N-methylanilino)-ethyl ester, to form monomer IX, e.g. to form the diazo compound of Example 2.5.
1-1.2 mol of the amino binuclear compound per mol of acid chloride is preferably used for reaction A. The reaction can be conducted in solvents, wherein inert organic solvents comprising ethers, e.g. dioxane, are preferred. The reaction is preferably conducted at temperatures from 20 to 80xc2x0 C.
The diazotisations for reactions B and C can be conducted in mineral acids such as hydrochloric acid, sulphuric acid or phosphoric acid for example, or can be conducted in carboxylic acids such as acetic acid or propionic acid, with sodium nitrite or nitrosylsulphuric acid as the nitrosylating agent, preferably at temperatures from xe2x88x9210 to +20, particularly 0 to +10xc2x0 C. In general, the coupling component is placed in a vessel, optionally in a suitable solvent such as glacial acetic acid or methanol, the pH is adjusted to a value from 1 to 6, preferably from 3 to 4, and the temperature during the addition of the diazonium component is maintained at 0 to 30, preferably 5 to 10xc2x0 C. The batch is then neutralised, with caustic soda or aqueous sodium carbonate solution for example, and is diluted with water, and the precipitated product is filtered off under suction.
The percentages given in the following examples are percentages by weight in each case unless indicated otherwise.